1. Field of the Invention
This invention relates to an integral plastic frame for holding a film slide, which frame comprises a central window, a recessed bearing surface, which surrounds the window and serves to contact the film slide when it has been inserted to cover the window, wherein the film slide as it is inserted and in its final position is guided between the bearing surface and the retaining elements facing the bearing surface, and the retaining elements substantially consist of continuous retaining strips, which extend in the direction in which the transparency is inserted.
2. Description of the Prior Art
Such frame has been disclosed in German Patent Specification No. 1,128,681. The known frame is provided on two mutually opposite sides of the central window with track grooves, which are defined by the bearing surface and the overlying wall portions and guide the film slide as it is inserted, the opening through which the film slide is inserted is offset from said grooves, and the film is flexible. It is not apparent from that printed publication whether the integral plastic slide frame is elastic. The projections might be replaced by overlying continuous wall portions, provided that they leave an opening through which the film slide can be inserted. But such frame could be made only by a complicated injection mold. When it is desired to remove a film slide which has been inserted, a hairpin or the like must be applied below the edge of the inserted film slide at the apex of a V-shaped edge so that the film slide can be lifted out. Such frame requires improvement in the following respects. The width of the opening through which the film slide can be inserted (corresponding to the height of the film bed) is too small for a mounting of cambered film, which may also be scratched as it is inserted. The free edges of the inserted film slide can easily curve upwardly, e.g., when the film slide is heated in a projector. The known frame cannot be used for an automatic mounting or such automatic mounting would be difficult.
German Patent Specification No. 700,519 discloses a frame which consists of two frame halves, which can be moved toward each other about a hinge. Such frame cannot be used for an automatic mounting because the frame cannot be closed until the cut film slide has been inserted. The film slide and the cover glass plates embedding the film slide are held by plate edges, which are bent in the same direction at right angles to a frame half and which constitute a receptacle for the film slide and the associated cover glass plates. A cambered film may slip from the position for projection before the frame is closed. The expenditure of material is about as high as for the frame in accordance with German Utility Model No. 72 34 660, which will be discussed hereinafter.
German Utility Model No. 1,815 522 discloses a holder for film sections. That holder comprises frame parts for receiving and holding the edge surface of the film sections. Said frame parts are constituted by an integral molding and the picture gate is laterally provided with a peripheral slot for receiving the film section. That slot is open on one side to form a opening through which a film section can be inserted into one frame part. That known frame involves a relatively high expenditure of material and can be made only by means of an expensive mold, which is liable to be deranged and comprises a slider mechanism. The film bed has a relatively large thickness (in excess of 0.3 mm) so that a proper fixation of the film in the frame is not ensured.
German Utility Model No. 72 34 660 discloses a plastic slide frame which comprises a frame member that is preferably provided with a continous peripheral rim and another frame part which consists of a flat cover and is preferably embedded within the frame member and is connected to the latter by a film hinge. That frame also involves a high expenditure of material and can be made only by an expensive mold because the frame when swung open has a very large projected area. The hinge is susceptible to damage. An additional operation for closing the frame is required. Expensive additional equipment consisting of an ultrasonic welder is required for closing the frame.